Inlay, inlay holder, method for tooth restoration, and tooth restoration set for carrying out the method

ABSTRACT

A prefabricated inlay (1) for restoring a tooth by application and fixation in a cavity prepared in the tooth and having essentially the same shape as the inlay part adapted for insertion, is provided with a pin (6) which projects from the inlay part not adapted for insertion and which is arranged to be received in an inlay holder. The whole inlay (1) is made of a material translucent to light that is suitable for curing a light-curing material used for fixing the inlay in the cavity. The inlay holder has a light source and a light guide having a tip (18) with a recess (19) for receiving the pin (6) of the inlay (1), such that the light generated by the light source can be guided through the light guide and the inlay (1) to the light-curing material. A tooth restoration set comprises a plurality of prefabricated frustoconical inlays (1), preferably having the same cone angle as well as several different narrow-end diameters, and a plurality of frustoconical burrs having the same cone angle as the inlays (1) as well as corresponding different narrow-end diameters.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

Generally, the present invention relates to tooth restoration.

More precisely, the invention concerns a prefabricated inlay forrestoring a tooth by application and fixation in a cavity prepared inthe tooth and having essentially the same shape as the inlay partadapted for insertion.

The invention also bears upon an inlay holder for the application of aprefabricated inlay in a cavity prepared in a tooth and havingessentially the same shape as the inlay part adapted for insertion.

The invention further encompasses a method for tooth restoration byapplying and fixing a prefabricated inlay in a cavity prepared in thetooth and having essentially the same shape as the inlay part adaptedfor insertion.

Finally, the invention relates to a tooth restoration set forimplementing the method.

2. Prior Art

Tooth restorations can be divided into indirect and direct restorations.In indirect restorations, an impression of a prepared cavity is made andemployed for producing an inlay of e.g. porcelain or gold. Suchrestorations have, inter alia, the disadvantage of being time-consuming,and thus necessitate at least two visits to the dentist. Also, theserestorations, which are fairly expensive, require the use of a temporaryfilling while the final inlay is being produced.

In direct restorations, use is commonly made of amalgam or compositematerials. The composite materials have been developed to replaceamalgam, but they are not suitable for large fillings, since they shrinkwhen cured, have a relatively low abrasion resistance and strength, andinvolve the risk of gaps arising in the interface between the fillingand the tooth.

Prefabricated inlays, preferably of ceramic material, have beendeveloped as a further alternative to amalgam fillings. By usingprefabricated inlays, a prepared cavity can be filled more or lesscompletely with the inlay which is fixed therein, e.g. by a compositematerial. With this technique, the effect of the shrinkage of thecomposite material is considerably reduced. However, a certain risk ofgap formation remains, unless the inlay covers the entire cavityopening. This also goes for the abrasion risk. Further, prior-arttechniques for applying and fixing a prefabricated inlay in a cavity areimperfect, in that they do not enable accurate positioning and rapidfixation of the inlay in the cavity.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is, therefore, to provide animproved prefabricated inlay, as well as improved techniques forapplying and fixing such an inlay in a prepared cavity.

According to the invention, this object is achieved by a prefabricatedinlay which is of the type mentioned by way of introduction, and whichis characterised in that it has a pin which projects from the inlay partnot adapted for insertion and which is arranged to be received in aninlay holder, and that the whole inlay is made of a material translucentto light that is suitable for curing a light-curing material used forfixing the inlay in the cavity. Since the pin can be received in aninlay holder, it is possible to have total control of the positioning ofthe inlay in the cavity. Owing to the fact that the inlay is made of theabove translucent material and the fact that a light-curing material isused for fixing the inlay in the cavity, fixation can be rapidlyperformed by guiding light via the inlay to the surrounding fixationmaterial in the cavity.

To achieve perfect control of the positioning of the inlay when insertedin the cavity, the pin conveniently has a round cross-sectional shape tobe received in an optional rotational position in a corresponding recessin the inlay holder.

For cavities that can be given a circular opening, the inlay accordingto the invention is conical and has the same cone angle as a burr usedfor preparing the cavity opening. Thus, the inlay can be made tocompletely fill at least the cavity opening, thereby eliminating therisk of gap formation. The material of the inlay then determinesabrasion resistance.

For cavities having a non-round opening, part of the opening may beround, in which case use is advantageously made of an at least partlyconical inlay with the same cone angle as a conical burr used forpreparing the cavity opening.

Advantageously, the inlay is made of a ceramic or glass-ceramicmaterial, suitably one that can be cast. When a conical inlay cannot beused, prefabricated inlays of other shapes, preferably a partly conicalshape, may of course be used.

The prefabricated inlays primarily serve to replace missing dentalenamel in the cavity, but they may also replace dentine to some extent.

The conical inlay, as well as the corresponding burr, preferably has theshape of a truncated cone. The inlay may, preferably closest to thenarrow end, be provided with one or more raised portions and/ordepressions serving to improve mechanical retention.

According to the invention, an inlay holder of the type mentioned by wayof introduction has a light source for generating light suitable forcuring a light-curing material for fixing the inlay in the cavity, and alight guide receiving the light from the light source and having a tipwith a recess adapted to receive a pin which projects away from theinlay part adapted for insertion, such that the light generated by thelight source can be guided through the light guide and the inlay to thelight-curing material. The inventive inlay holder enables securepositioning of the inlay in the cavity. Since the inlay holder isintegrated with the light guide for the curing light, extremely rapidfixation of the inlay in the cavity can be attained. Among other things,this is necessary in order to prevent the formation of gaps at theinterfaces between the fixation material and, respectively, the inlayand the tooth. The inlay holder may easily be produced by modifying aconventional curing lamp.

The rotational position of the inlay in relation to the inlay holder canbe varied by giving the recess in the light-guide tip a roundcross-sectional shape. Then, the pin of the inlay should have the sameround cross-sectional shape.

In a preferred embodiment, the light source of the inlay holdergenerates blue light in the wave range of 400-500 nm. The light sourcemay be a halogen light source or a laser light source.

According to the invention, the method for restoration mentioned by wayof introduction is characterised by preparing at least a portion of thecavity opening by means of a conical burr so as to impart an at leastpartly conical shape to this portion; and applying and fixing in thecavity an inlay which has a part corresponding to said portion andhaving exactly the same cone angle as the conical burr. With thismethod, the cavity opening will be completely filled with the conicalinlay, especially when entirely conical. The risk of shrinkage and gapformation is thus almost completely eliminated.

In a preferred mode of operation, a pin projecting from the thick end ofthe inlay is inserted in a corresponding recess in an inlay holder; theinlay is fixed in the cavity by means of a light-curing material; andlight for curing this material is guided through the inlay holder andthe inlay. It is to be understood that the inventive method enables veryaccurate positioning and extremely rapid fixation of the inlay in thecavity.

Conveniently, the preferably pre-etched inlay is silanised prior toapplication in the cavity.

According to the invention, a tooth restoration set for implementing theabove method is characterised by a plurality of prefabricatedfrustoconical inlays, preferably having the same cone angle as well asseveral different narrow-end diameters, and a plurality of frustoconicalburrs having the same cone angle as the inlays as well as correspondingdifferent narrow-end diameters. Preferably, the number of burrs in theset is smaller than the number of conical inlays but yet sufficient fora burr of each type always to be available, regardless of thesterilisation of used burrs required.

Preferably, each inlay in the set has a pin which projects from thethick end and is adapted to be received in an inlay holder provided witha recess designed to receive the pin.

To enable contactless handling, the inlays are suitably fixed in acontainer in such a position that they can be removed therefrom by meansof the inlay holder alone.

Preferably, the burrs are diamond burrs which are diamond-coated also onthe end surface of the narrow end. Further, the inlays are preferablytranslucent to light that is suitable for curing a light-curing materialused for fixing an inlay in a tooth cavity.

It will be appreciated that the present invention encompassing theprefabricated inlay, the inlay holder, the restoration method and therestoration set involves considerable improvements in direct toothrestorations. Thus, the invention enables tooth restoration to beperformed in a very short time. Further, the restoration according tothe invention is of high quality as to appearance as well as durability.As a result of the short time required and the materials used, the costsfor performing a tooth restoration with the aid of the invention can bekept quite low.

The fact that the cavity should have essentially the same shape as theinlay part adapted for insertion is to be understood to mean that atleast the opening part of the cavity and the corresponding inlay partshould have a substantially mating shape.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference tothe accompanying drawing, in which

FIG. 1 is a side view of three prefabricated inlays according to theinvention;

FIG. 2 is a side view of three corresponding burrs according to theinvention used for preparing a cavity for inlays of the type shown inFIG. 1;

FIG. 3 is a perspective view of another embodiment of an inlay accordingto the invention;

FIG. 4 is a side view of an inlay holder according to the invention;

FIG. 5 is a detail view of a light-guide tip of the inlay holder in FIG.4; and

FIG. 6 is a perspective view illustrating the method according to theinvention.

FIG. 1 shows prefabricated, inventive inlays 1-3 which are made of aceramic or glass-ceramic material whose properties are as similar tothose of dental enamel as possible. This material should preferably becastable or industrially sintered, so that the inlays 1-3 may easily beproduced in large series of high dimensional accuracy. The inlays 1-3have a frustoconical part 4 having a circular cross-section and beingadapted for insertion into a cavity in a tooth. At the narrow end of thefrustoconical part 4, the inlays 1-3 have a recess in the form of acircumferential groove 5 serving to improve the mechanical retention ofthe inlay when this has been applied in the tooth cavity. Alternatively,the inlays 1-3 may, for the same purpose, be provided with raisedportions which, however, must not project radially to such an extentthat the inlays 1-3 cannot be inserted in the cavity at issue. Neitherthe depressions nor the raised portions are compulsory, since theretention needed can often be achieved all the same, especially if theinlays are etched. The thick end of the conical inlays 1-3, i.e. theinlay part not adapted for insertion, has an axially projecting pin 6 ofpreferably round cross-section.

The narrow end of the conical part 4 preferably has a rounded shape.

In a preferred embodiment, the cone angle of the frustoconical part 4 isapproximately 28°. Naturally, the invention is not restricted to thisangle, but encompasses other cone angles as well. In differentembodiments, the inlays 1-3 can have different diameters at the narrowend but essentially the same height at the frustoconical part 4, asillustrated in FIG. 1.

FIG. 2 is a side view of three different, frustoconical burrs 7-9.Preferably, the burrs 7-9 have a diamond coating both on thecircumferential surface of the frustoconical part and on the end surfaceof the narrow end. To enable mounting in conventional drillingequipment, the burrs 7-9 have a shank 10 projecting axially from thethick end. According to the invention, the cone angle of the burrs 7-9should be identical with that of the corresponding inlays 1-3 that areto be applied in cavities prepared by the burrs.

FIG. 3 shows another embodiment of an inlay 11 according to theinvention. This inlay 11 is substantially L-shaped and has, inaccordance with the invention, two lateral surfaces 12, 13, which eitherare parallel or converge slightly downwards, on one branch of the L.This branch, which is to be contained in the occlusal part of thecavity, has, in accordance with the invention, a conical end 12a, i.e. apartly conical portion. Alternatively, the end 12a may be partlycylindrical and be inclined obliquely inwards-downwards. The inlay 11 isintended to for making a "class II" filling, in which case the abovebranch is to be accommodated in an occlusal part of the cavity, whilethe other branch of the L is to be accommodated in a proximal part ofthe cavity. A pin 14 projects upwards from the future outer part of theocclusal surface of the inlay 11 at an acute angle to the branch withthe lateral surfaces 12, 13. Conveniently, the pin 14 has the same shapeas the pin 6 in FIG. 1, and the inlay 11 is made of the same material asthe inlays 1-3 in FIG. 1. By angling the pin 14, the inlay 11 may, whenapplied, be simply pressed against both the occlusal opening edges ofthe cavity and the adjoining tooth, thereby optimising positioning ofthe inlay 11 in the cavity, by the forces that act on the inlay 11 afterrestoration being directly transferred to the underlying original toothmaterial. By the special design of the end 12a, the inlay can, whenapplied, be axially displaced, and consequently in mesiodistaldirection, to optimise positioning in the cavity.

The embodiment of an inlay holder according to the invention shown inFIG. 4 consists of a conventional curing lamp 15 containing a lightsource 16, e.g. a halogen or laser light source, for generating lightsuitable for curing a light-curing material in order to fix e.g. theinlay 1 in a cavity prepared therefor. Further, the curing lamp 15 has alight guide 17 extending from the light source 16 out into a tip 18. Asillustrated in more detail in FIG. 5, a recess or hole 19 is, inaccordance with the invention, provided in the free end of thelight-guide tip 18 and has a cross-sectional shape corresponding to thatof the pins 6, 14. This recess may be slightly conical, so that, aftere.g. the pin 6 has been inserted therein, e.g. the inlay 1 is retainedin a fixed position in the light-guide tip 18, there being goodtransmission from the light-guide tip 18 of the light generated by thelight source 16 into the pin 6 and through the whole inlay 1.

The method according to the invention will now be described withreference to FIG. 6, involving the use of an inlay 1 of the type shownin FIG. 1 for the restoration of an occlusal cavity 20 in a tooth 21. Ina first step, the cavity 20 is prepared by drilling its interior to asufficient extent. Then, the opening of the cavity 20 is prepared bymeans of a burr of the type shown in FIG. 2. These steps may also beperformed in the reverse order. Then, the internal surface of the cavityis insulated by a suitable insulating material, e.g. a glass ionomer. Ifa non-conical inlay, e.g. an inlay of the type shown in FIG. 3, is to beemployed, a gauge can be used for determining the size and the shape ofthe inlay. In the case described, use is made of a conical inlay 1 witha size corresponding to the burr used. Preferably, this inlay ispre-etched, and is cleaned, dried and silanised after being fixed in theinlay holder. Prior to the application of the inlay 1 in the cavity 20,the latter may be etched with phosphoric acid and, after drying, befilled with a fixing material, e.g. a light-curing composite material.Preferably, use is made of a dual composite which is not only slowlychemically curing but also rapidly light-curing. Immediately beforeapplication of the inlay 1 in the cavity, the inlay part adapted forinsertion can be wetted with a resin. Then, the inlay 1 is pressed downinto the cavity 20 until its circumferential surface makes firm contactwith the opening of the cavity 20, whereupon the light source 16 of theinlay holder 15 is lit for rapid curing of the composite material,thereby fixing the inlay 1 in the cavity 20. The inlay holder 15 maythen be removed by pulling the tip 18 off the pin 6. Alternatively, thepin 6 can be broken by means of the inlay holder 15. Finally,restoration is completed by grinding and polishing the exposed part ofthe inlay 1 to the desired shape and finish.

It goes without saying that several modifications of the embodimentsdescribed above are conceivable within the scope of the invention asdefined in the appended claims.

We claim:
 1. A method for restoring a tooth by applying and fixing aprefabricated inlay (1; 11) in a cavity (20) prepared in the tooth andhaving essentially the same shape as the inlay adapted for insertion,comprising the steps of preparing at least a portion of the cavity bymeans of a conical burr (7-9) so as to impart an at least partly conicalshape to said portion; and applying and fixing in the cavity an inlay(1; 11) which has a part corresponding to said portion and having thesame cone angle as the conical burr.
 2. A method as claimed in claim 1including the steps of making the opening of the cavity (20) entirelyconical; and applying and fixing a conical inlay (1) in the cavity.
 3. Amethod as claimed in claim 1, wherein said inlay further comprises a pinand including the steps of inserting said pin (6), which projects awayfrom a thick end of the inlay (1), into an inlay holder (15) having acorresponding recess (19); fixing the inlay in the cavity (20) by meansof a light-curing material; and guiding light for the curing of saidmaterial through the inlay holder (15) and the inlay (1).
 4. A method asclaimed in claim 1, wherein said inlay is pre-etched including the stepof silanising said pre-etched inlay (1) prior to application.
 5. A toothrestoration set, comprising a plurality of prefabricated frustoconicalinlays (1), each having the same cone angle as well as a differentdiameter at a narrow-end, and a plurality of frustoconical burrs (7-9)having the same cone angle as the inlays (1) as well as correspondingdifferent diameter at a narrow-end.
 6. A set as claimed in claim 5,wherein each inlay (1) has a pin (6) which projects away from a thickend and is receivable in an inlay holder.
 7. A set as claimed in claim5, wherein the inlays (1) are fixed in a container in such a positionthat they can be removed from the container by means of an inlay holder(15) alone.
 8. A set as claimed in claim 5, wherein the burrs (7-9) arediamond burrs which are each diamond-coated on an end surface of thenarrow end.
 9. A set as claimed in claim 5, wherein the inlays (1) aretranslucent to a light that is suitable for curing a light-curingmaterial used to fix an inlay in a tooth cavity.